1. Field of the Invention
The present invention relates to the use of a pulse wave generated around an artery of a human body. More particularly, the present invention relates to a method and apparatus for acquiring a pulse wave signal and an electrocardiogram (ECG) signal using a pressure sensor, an infrared sensor, and an electrode and providing an analyzed result as a blood pressure value of an artery of a brachium.
2. Description of the Related Art
The occurrence of diseases related to high blood pressure such as heart disease and strokes has been shown to increase with a decrease of physical activity and a correlation with certain dietary habits. On the other hand, one of reasons that the importance of preventing diseases related to high blood pressure in society is that the occurrence of diseases related to high blood pressure rapidly increases with an increase in age. One of the methods of diagnosing and preventing the occurrence of diseases related to high blood is to periodically measure blood pressure. Arterial blood pressure is determined by the flow of blood, the elasticity of a blood vessel, contraction resistance, etc., and is a vital sign indicating an abnormal symptom in organs related to high blood pressure. High blood pressure can damage all major organs in the body.
There are two basic methods of measuring blood pressure, i.e. an invasive method and a non-invasive method. When a high-risk patient is being treated in an Operating Room (OR) or an Intensive Care Unit (ICU), the invasive method, which can continuously monitor arterial blood pressure and take an arterial blood sample on demand for analyzing gas of the arterial blood, is used. However, the invasive method is very cumbersome in preparation and treatment, may cause a complication such as damage to tissues due to infection or blood vessel obstruction. In addition, as the invasive method, is mostly applied to critically ill patients, and patient management in such cases requires a great deal of care use, there is a concern regarding complications associate with use of the invasive method. Thus, under ordinary circumstances, the non-invasive method of measuring blood pressure using a cuff is mainly used. However, the non-invasive method has disadvantages that blood pressure cannot be continuously monitored, a difference may occur according to subjectivity of the person taking the measurement, etc. Also, there is difficulty in measuring blood pressure in the case where the blood pressure decreases to less than a predetermined value. For example, it has been reported that it is difficult to apply the non-invasive method to children and critically ill patients, and accuracy of the non-invasive method is significantly lower for patients having diastolic blood pressure of 70 mm Hg.
In addition, there is another disadvantage in that correct blood pressure measurements cannot be obtained if the circumference of a brachium wrapped by a cuff is not factored into a blood pressure measurement using a cuff. However, at present, it is impossible to measure blood pressure with a cuff and factor in the circumference of a brachium. Moreover, since a process of applying pressure of around 200 mmHg is necessary when a cuff is used, a blood vessel or tissue may be damaged from the pressure. In order to compensate these disadvantages due to a cuff, there have been unsuccessful attempts to continuously measure blood pressure via a non-invasive method without the use of the cuff. However, reliable blood pressure monitoring under such circumstances has not been realized.
Attempts at providing apparatuses for continuously measuring non-invasive and cuffless blood pressure are disclosed in U.S. Pat. No. 6,413,223 titled “Cuffless Continuous Blood Pressure Monitor” and U.S. Pat. No. 6,669,648 titled “Continuous Non-invasive Sphygmo-manometer”. However, such measured positions are limited to a finger, or blood pressure is measured at a position around a wrist, which is difficult to affix. Moreover, since such as the apparatus as disclosed in the aforementioned patent requires additional devices for driving a light source to continuously measure blood pressure, such apparatuses fail to solve a problem that it is inconvenient and difficult to apply the such apparatuses to a human body in order to make an accurate measurement.
As the measurement of blood pressure provides important diagnostic information and is a factor in the treatment of patients for many illnesses, there is a long-felt need in the art to develop a technique of simply and continuously measuring blood pressure at a wrist without using a cuff. There are many obstacles that must be overcome, such as the deployment of a sensor attached to the human body, the establishment of a correct algorithm for calculating blood pressure values using a waveform of a pulse wave, easy attachment and detachment of such an apparatus, and portability.